From: Matthew Kerwin <matthew@...>
Date: 2012-06-13T13:21:06+09:00
Subject: Re: Problem with reg exp

Sorry, I realise I should have probably given some code to exemplify
what's in my head:

  str1 = "ABC12A2012"
  if str1 =~ /^([a-zA-Z]+)(.*?)(?:KEYWORD)?$/
    p $1, $2 # => "ABC", "12A2012"
  end

  str2 = "ABC13B2012KEYWORD"
  if str2 =~ /^([a-zA-Z]+)(.*?)(?:KEYWORD)?$/
    p $1, $2 # => "ABC", "13B2013"
  end

To get it to work I:
* made a non-capturing group, using the (?: ... ) syntax, so the
entire string 'KEYWORD' can be marked as optional.
* made the middle _anything_ matcher (.*) non-greedy (so it doesn't
automatically also capture a trailing KEYWORD) by appending a question
mark
* tacked a $ end-of-string marker after the optional KEYWORD thing, to
ensure that the non-greedy _anything_ matcher actually matches;
otherwise it seems quite happy to match ""
* also put a ^ start-of-string marker, since my if-statement is
simultaneously validating the string as well as extracting the match.
It doesn't really do anything, you can leave it out.

You could also wrap the non-capturing keyword group in capturing
parens if you want to extract the keyword, thus:

  str1 = "ABC12A2012"
  if str1 =~ /^([a-zA-Z]+)(.*?)((?:KEYWORD)?)$/
    p $1, $2, $3 # => "ABC", "12A2012", ""
  end

  str2 = "ABC13B2012KEYWORD"
  if str2 =~ /^([a-zA-Z]+)(.*?)((?:KEYWORD)?)$/
    p $1, $2, $3 # => "ABC", "13B2013", "KEYWORD"
  end

If you don't like using the if-statement structure, you can also use
String#match , which returns a MatchData object. You can access the
groups using array syntax:

  str1 = "ABC12A2012"
  md = str1.match /^([a-zA-Z]+)(.*?)((?:KEYWORD)?)$/
  p md[1] => "ABC"
  p md[2] => "12A2012"

etc.

String#split , on the other hand, breaks the string up by chopping out
any parts of the string that match the regexp, and returning the
remaining chunks as an array.  For example:

  str2.split /[0-9]+/  # => ["ABC", "B", "KEYWORD"]

That is, it chops out the numbers, and returns the bits in between.

I'd have to think a lot harder about how you're getting what you're
getting with str2, but I'm already pretty sure the actual question can
be resolved using =~ or String#match

On 13 June 2012 11:30, cyber c. <lists@ruby-forum.com> wrote:
> Hi,
>
> I need to match
>
> str1 = "ABC12A2012"
> str2 = "ABC13B2013KEYWORD"
>
> i have to extract,
> word1 = ABC, word2 = 12A2012 for str1
> word1 = ABC, word2 = 13B2013 for str2
>
> i have used
> str.split(/([a-zA-Z]+)(.*)(KEYWORD?)/)
>
> for str2 i get substrings as
> "","ABC","12A2012","KEYWORD" --  Why did the nil sub string popped up?
>
> for str1 i get only 1 substring which is the entire string
>
> Any one can spot the problem , please let me know.
>
> --
> Posted via http://www.ruby-forum.com/.
>



-- 
  Matthew Kerwin, B.Sc (CompSci) (Hons)
  http://matthew.kerwin.net.au/
  ABN: 59-013-727-651

  "You'll never find a programming language that frees
  you from the burden of clarifying your ideas." - xkcd